Percutaneous Transluminal Coronary Angioplasty (PTCA), an operation which widens the lumen of narrowed parts in blood vessels to ameliorate the blood flow using a catheter with a dilatation element, is practiced as a method of treating stenosis. Catheters with a dilatation element, such as those of the so called "over the wire" type, as disclosed in the specification of U.S. Pat. No. 4,323,071, which are guided over a guide wire passed freely through their interior opening, are used for PTCA. In recent years, however, a need of lowprofile catheters is increasing for treating stenosis in more peripheral side blood vessels. But the conventional catheters, for its structure, cannot be made sufficiently lowprofile to pass through such narrow stenotic lesions and cannot cope with this need. Then, the catheter of the so called "on the wire" type, whose dilatation element is directory attached on the guide wire, as disclosed in the specification of U.S. Pat. No. 4,77,778, was devised and is becoming able to treat such difficult cases for its structural advantage that it can be made very lowprofile.
Though the "on the wire" type catheter as disclosed in U.S. Pat. No. 4,771,778 has become able to pass through stenotic lesions in narrow vessels that conventional catheters cannot pass through, it has problems of its own. Since its dilatation element is directly attached on the guide wire, turn of the guide wire can twist and damage the dilatation element. Therefore, the very function of the guide wire, that is, to be turned to enter into a desired vessel, is considerably restricted. Thus, the manipulatability of this type of catheter is lower than that of the conventional "over the wire" type catheters, and it is sometimes difficult to enter the guide wire into a aimed branch vessel.
On the other hand, the catheter disclosed by U.S. Pat. No. 4,616,653 has the dilatation element attached on the catheter body and the guide wire housed in the catheter body as in the conventional "over the wire" type catheter, and its guide wire can be turned freely. However, this type of catheter has a disadvantage that it cannot not be made so thin as the "on the wire" type catheter. Further, since this type of catheter has two lumens, one for passing the guide wire and another for injecting a dilatation liquid into the dilatation element, the liquid lumen cannot be made sufficiently wide and liquid injection is difficult if the catheter body is made very thin as required; on the other hand, the catheter body cannot be made sufficiently thin if the liquid lumen is made so wide so to facilitate liquid injection, though the manipulatability of this type of catheter is very high.
The object of the present invention is to provide a blood vessel dilator which is so thin in outside diameter as the "on the wire" type catheter retaining a sufficiently wide liquid lumen and is highly manipulatable at branched parts of blood vessels by a separately turnably guide wire and hence can be readily inserted even into narrow peripheral blood vessels, in order to solve the above problems of the prior art.